Process for treating hard tissues

ABSTRACT

In a first aspect, a method for treating hard tissue that includes: (a) applying to hard tissue a composition that includes a cationically active functional group, a free radically active functional group, and a polymerization initiator capable of initiating free radical polymerization, where the number of moles of cationically active functional groups per gram of composition is no greater than about 0.0075; and (b) exposing the composition to polymerization conditions to form an adhesive bonded to the hard tissue. 
     In a second aspect, a method for treating hard tissue that includes: (a) applying to hard tissue a first polymerizable composition that includes a free radically active functional group and a polymerization initiator capable of initiating free radical polymerization, but is essentially free of polymerizable components having cationically active functional groups and is capable of forming an adhesive bonded to the hard tissue upon exposure to polymerization conditions; (b) applying a second polymerizable composition; and (c) exposing the second composition to polymerization conditions to form a hardened composition adhered to the hard tissue. The second composition includes (i) a cationically active functional group and (ii) an polymerization initiator capable of initiating cationic polymerization.

This is a continuation of application Ser. No. 09/055,885 filed Jan. 12,1998, now U.S. Pat. No. 5,980,253.

BACKGROUND OF THE INVENTION

This invention relates to treating hard tissues such as tooth enamel ordentin.

Dental compositions such as composites, sealants, and cements generallywill not bond sufficiently to tooth enamel or dentin unless the enamelor dentin is pre-treated with an adhesive layer. Typically, the enamelis etched with an acidic solution, followed by application of anunfilled methacrylate-based pre-adhesive composition that is polymerizedusing a thermally or photochemically activated free radical initiatorsystem to form a layer of adhesive. The dental composition, which istypically a filled methacrylate-based composition, is then placed overthe adhesive and polymerized using a free radical initiator system toform a hard, wear-resistant material. The adhesive, therefore, bonds toboth the acid-etched tooth and to the dental composition.

Methacrylate-based dental compositions exhibit a relatively high degreeof volumetric shrinkage upon polymerization. Accordingly, cationicallycurable compositions, and hybrid compositions featuring bothcationically and free radically curable components, have been suggestedas alternatives. Such compositions, which typically include epoxy resinsas the cationically curable component, exhibit less shrinkage upon curethan the methacrylate-based compositions.

SUMMARY OF THE INVENTION

The inventors have discovered that pre-adhesive compositions containingrelatively large amounts of cationically curable groups do not bond wellto hard tissues such as tooth enamel and dentin. It is believed that thetooth inhibits polymerization of such materials. On the other hand, inthe case of cationically curable dental compositions, conventionalwisdom would dictate that it is desirable for the adhesive to contain asubstantial number of cationically curable groups as well.

The inventors have discovered two ways of attacking this problem. Oneapproach is to prepare a hybrid pre-adhesive composition that includesfree radically active functional groups and a limited amount ofcationically active functional groups. The inventors have discoveredthat such compositions successfully polymerize on the surface of hardtissue to form a strong bond with the hard tissue, yet at the same timecan successfully bond to compositions that include cationically activegroups.

The second approach is to eliminate cationically active groupsaltogether from the pre-adhesive composition, but engineer thepre-adhesive composition so that it still bonds to a subsequentlyapplied composition that includes cationically active groups.Preferably, this is accomplished by incorporating functional groups suchas hydroxyl groups in the pre-adhesive composition that can covalentlybond to the subsequently applied composition.

In both approaches, the compositions are preferably free of componentsin amounts that would detrimentally affect polymerization of thecationically active functional groups of the pre-adhesive composition,polymerization of a subsequently applied cationically polymerizablecomposition, or both.

Accordingly, in a first aspect, the invention features a method fortreating hard tissue that includes: (a) applying to hard tissue acomposition that includes a cationically active functional group, a freeradically active functional group, and a polymerization initiatorcapable of initiating free radical polymerization, where the number ofmoles of cationically active functional groups per gram of compositionis no greater than about 0.0075; and (b) exposing the composition topolymerization conditions to form an adhesive bonded to the hard tissue.Preferably, the number of moles of cationically active functional groupsis no greater than about 0.002. Prior to treatment with the composition,the hard tissue may be treated with an agent selected from the groupconsisting of etchants, primers, adhesion promoters, and combinationsthereof.

As used herein, a "cationically active functional group" refers to achemical moiety that is activated in the presence of an initiatorcapable of initiating cationic polymerization such that it is availablefor reaction with other compounds bearing cationically active functionalgroups. A "free radically active functional group" refers to a chemicalmoiety that is activated in the presence of an initiator capable ofinitiating free radical polymerization such that it is available forreaction with other compounds bearing free radically active functionalgroups.

The composition is preferably exposed to visible light in order to formthe adhesive bonded to the hard tissue; the composition may also beauto-cured. The strength of the bond formed between the adhesive and thehard tissue preferably is at least about 3 MPa. The method isparticularly useful where the hard tissue is a tooth (e.g., tooth enamelor dentin).

Suitable components of the composition include epoxy resins (whichcontain cationically active epoxy groups) and ethylenically unsaturatedcompounds (which contain free radically active unsaturated groups),preferably in combination with each other. Examples of usefulethylenically unsaturated compounds include acrylic acid esters,methacrylic acid esters, and combinations thereof. Also suitable arepolymerizable components that contain both a cationically active groupand a free radically active group in a single molecule. Examples includeepoxy-functional acrylic acid esters, methacrylic acid esters, andcombinations thereof.

The composition may also include a hydroxy-functional component. Thehydroxy functional group may be present in combination with anethylenically unsaturated group, e.g., in the form of ahydroxy-functional acrylic acid ester, a hydroxy-functional methacrylicacid ester, or combination thereof, or in combination with acationically active functional group such as an epoxy. It may also bepresent in the form of a separate molecule, e.g., a polyol such as apolyether polyol.

Suitable polymerization initiators include initiators that initiatepolymerization of free radically active functional groups. Suchinitiators may additionally initiate polymerization of cationicallyactive functional groups.

One example of a suitable polymerization initiator includes an iodoniumsalt, preferably in combination with a visible light sensitizer.Particularly preferred are initiators that include an iodonium salt, avisible light sensitizer, and an electron donor in which the initiatorhas a photoinduced potential greater than or equal to that of3-dimethylamino benzoic acid in a standard solution of 2.9×10⁻⁵ moles/gdiphenyl iodonium hexafluoroantimonate and 1.5×10⁻⁵ moles/gcamphorquinone in 2-butanone. Also suitable are auto-cure initiatorsthat rely upon a chemical reaction, e.g,. between a peroxide and anamine to trigger the polymerization process.

The method may further include applying a dental material (e.g., adental composite such as a dental restorative) to either the adhesive orto the composition prior to polymerization. In the latter case,polymerization to form the adhesive takes place subsequent toapplication of the dental material. For example, polymerization to formthe adhesive may take place concurrently with polymerization of thedental material. An example of a useful dental material is a dentalcomposite that includes a cationically active functional group, apolymerization initiator (e.g., an iodonium salt), and a filler; thecomposite may further include a free radically active functional group.

The invention further features a kit that includes the above-describedcomposition and a dental material capable of bonding to the adhesive.The dental material may be a dental composite such as a dentalrestorative. Preferably, the dental composite includes a cationicallyactive functional group, a polymerization initiator, and a filler. Thedental composite may include a free radically active functional group aswell.

The invention also features a hard tissue sample such as a tooth havinga surface treated with the above-described bonding composition.

In a second aspect, the invention features a method for treating hardtissue that includes: (a) applying to hard tissue a first polymerizablecomposition that includes a free radically active functional group and apolymerization initiator capable of initiating free radicalpolymerization, but is essentially free of polymerizable componentshaving cationically active functional groups; (b) applying a secondpolymerizable composition; and (c) polymerizing the second compositionto form a hardened composition adhered to the hard tissue. The secondcomposition includes (i) a cationically active functional group and (ii)an polymerization initiator capable of initiating cationicpolymerization.

The first composition is capable of forming an adhesive bonded to thehard tissue upon exposure to polymerization conditions. Polymerizationto form the adhesive may take place prior to application of the secondcomposition, or subsequent to application of the second composition. Forexample, in the latter case polymerization to form the adhesive may takeplace concurrently with polymerization of the second composition. Priorto treatment with the first polymerizable composition, the hard tissuemay be treated with an agent selected from the group consisting ofetchants, primers, adhesion promoters, and combinations thereof.

The method is particularly useful where the hard tissue is a tooth(e.g., tooth enamel or dentin). In such cases, the second compositionpreferably is a dental material, e.g., a dental composite such as adental restorative.

The first composition preferably includes a functional group capable ofcovalently bonding to the second composition. An example of such afunctional group is a hydroxyl group. The functional group may bepresent in the form of a separate molecule (e.g., a polyol). It may alsobe present in the form of a molecule that includes a free radicallyactive or cationically active functional group as well. Examples of theformer include hydroxy-functional acrylic acid esters,hydroxy-functional methacrylic acid esters, and combinations thereof,whereas examples of the latter include hydroxy-functional epoxy resins.

The second composition preferably includes an epoxy resin (whichcontains cationically active groups). It may also include a freeradically active functional group, e.g., in the form of an acrylic acidester, a methacrylic acid ester, or a combination thereof. The secondcomposition may also include a component that includes both acationically active functional group and a free radically activefunctional group in a single molecule. Examples of such componentsinclude epoxy-functional acrylic acid esters, epoxy-functionalmethacrylic acid esters, and combinations thereof.

At least one of the initiators may include an iodonium salt, preferablyin combination with a visible light sensitizer. Particularly preferredare initiators that include an iodonium salt, a visible lightsensitizer, and an electron donor in which the initiator has aphotoinduced potential greater than or equal to that of 3-dimethylaminobenzoic acid in a standard solution of 2.9×10⁻⁵ moles/g diphenyliodonium hexafluoroantimonate and 1.5×10⁻⁵ moles/g camphorquinone in2-butanone.

The invention further features a kit that includes the above-describedfirst and second polymerizable compositions according to the secondaspect of the invention, as well as a hard tissue sample such as a toothhaving a surface treated with these two compositions.

The invention provides adhesives prepared from compositions havinglimited numbers of cationically active groups, or no cationically activegroups, that adhere well to hard tissue such as tooth enamel and dentin.Such adhesives also adhere well to both cationically polymerizable andfree radically polymerizable compositions, particularly where theadhesive contains functional groups such as hydroxyl groups that arecapable of covalently bonding to the cationically polymerizable or freeradically polymerizable composition. The adhesives are useful in avariety of applications, including bonding dental compositions such asdental composites to tooth enamel or dentin, particularly where thedental composition includes a cationically polymerizable component suchas an epoxy resin.

Other features and advantages of the invention will be apparent from thefollowing description of the preferred embodiments thereof, and from theclaims.

DETAILED DESCRIPTION

Adhesive Bonding Compositions

Adhesive bonding compositions are prepared from pre-adhesivecompositions having a free radically active functional group and eitherlimited amounts of cationically active functional groups, or nocationically active functional groups. Preferably, the number of molesof cationically active functional groups per gram of pre-adhesivecomposition is no greater than about 0.0075, more preferably no greaterthan about 0.002. The pre-adhesive composition also preferably containsfunctional groups such as hydroxyl groups capable of covalently bondingto a subsequently applied composition such as a dental composite,sealant, or cement. In addition, the pre-adhesive compositions arepreferably free of components in amounts that would detrimentally affectpolymerization of the cationically active functional groups of thepre-adhesive composition, polymerization of a subsequently appliedcationically polymerizable composition, or both.

Materials having free radically active functional groups includemonomers, oligomers, and polymers having one or more ethylenicallyunsaturated groups. Suitable materials contain at least oneethylenically unsaturated bond, and are capable of undergoing additionpolymerization. Such free radically polymerizable materials includemono-, di- or poly-acrylates and methacrylates such as methyl acrylate,methyl methacrylate, ethyl acrylate, isopropyl methacrylate, n-hexylacrylate, stearyl acrylate, allyl acrylate, glycerol diacrylate,glycerol triacrylate, ethyleneglycol diacrylate, diethyleneglycoldiacrylate, triethyleneglycol dimethacrylate, 1,3-propanedioldiacrylate, 1,3-propanediol dimethacrylate, trimethylolpropanetriacrylate, 1,2,4-butanetriol trimethacrylate, 1,4-cyclohexanedioldiacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate,pentaerythritol tetramethacrylate, sorbitol hexacrylate,bis[1-(2-acryloxy)]-p-ethoxyphenyldimethylmethane, bis[1-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylmethane, andtrishydroxyethyl-isocyanurate trimethacrylate; the bis-acrylates andbis-methacrylates of polyethylene glycols of molecular weight 200-500,copolymerizable mixtures of acrylated monomers such as those in U.S.Pat. No. 4,652,274, and acrylated oligomers such as those of U.S. Pat.No. 4,642,126; and vinyl compounds such as styrene, diallyl phthalate,divinyl succinate, divinyl adipate and divinylphthalate. Mixtures of twoor more of these free radically polymerizable materials can be used ifdesired.

Materials having cationically active functional groups includecationically polymerizable epoxy resins. Such materials are organiccompounds having an oxirane ring, i.e., a group of the formula ##STR1##which is polymerizable by ring opening. These materials includemonomeric epoxy compounds and epoxides of the polymeric type and can bealiphatic, cycloaliphatic, aromatic or heterocyclic. These materialsgenerally have, on the average, at least 1 polymerizable epoxy group permolecule, preferably at least about 1.5 and more preferably at leastabout 2 polymerizable epoxy groups per molecule. The polymeric epoxidesinclude linear polymers having terminal epoxy groups (e.g., a diglycidylether of a polyoxyalkylene glycol), polymers having skeletal oxiraneunits (e.g., polybutadiene polyepoxide), and polymers having pendentepoxy groups (e.g., a glycidyl methacrylate polymer or copolymer). Theepoxides may be pure compounds or may be mixtures of compoundscontaining one, two, or more epoxy groups per molecule. The Aaverage™number of epoxy groups per molecule is determined by dividing the totalnumber of epoxy groups in the epoxy-containing material by the totalnumber of epoxy-containing molecules present.

These epoxy-containing materials may vary from low molecular weightmonomeric materials to high molecular weight polymers and may varygreatly in the nature of their backbone and substituent groups. Forexample, the backbone may be of any type and substituent groups thereoncan be any group that does not substantially interfere with cationicpolymerization at room temperature. Illustrative of permissiblesubstituent groups include halogens, ester groups, ethers, sulfonategroups, siloxane groups, nitro groups, phosphate groups, and the like.The molecular weight of the epoxy-containing materials may vary fromabout 58 to about 100,000 or more.

Useful epoxy-containing materials include those which containcyclohexene oxide groups such as epoxycyclohexanecarboxylates, typifiedby 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate,3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexanecarboxylate, and bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate. For amore detailed list of useful epoxides of this nature, reference is madeto the U.S. Pat. No. 3,117,099, which is incorporated herein byreference.

Further epoxy-containing materials which are useful in the compositionsof this invention include glycidyl ether monomers of the formula##STR2## where R= is alkyl or aryl and n is an integer of 1 to 6.Examples are glycidyl ethers of polyhydric phenols obtained by reactinga polyhydric phenol with an excess of chlorohydrin such asepichlorohydrin (e.g., the diglycidyl ether of2,2-bis-(2,3-epoxypropoxyphenol)-propane). Further examples of epoxidesof this type are described in U.S. Pat. No. 3,018,262, which isincorporated herein by reference, and in Handbook of Epoxy Resins by Leeand Neville, McGraw-Hill Book Co., New York (1967).

There are a host of commercially available epoxy resins which can beused in this invention. In particular, epoxides which are readilyavailable include octadecylene oxide, epichlorohydrin, styrene oxide,vinyl cyclohexene oxide, glycidol, glycidylmethacrylate, diglycidylether of Bisphenol A (e.g., those available under the trade designationsEpon 828™, Epon 825™, Epon 1004™ and Epon 1010™ from Shell Chemical Co.,DER-331™, DER-332™, and DER-334™, from Dow Chemical Co.),vinylcyclohexene dioxide (e.g., ERL-4206™ from Union Carbide Corp.),3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexene carboxylate (e.g.,ERL-4221™ or CYRACURE UVR 6110™ or UVR 6105™ from Union Carbide Corp.),3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methyl-cyclohexenecarboxylate (e.g., ERL-4201™ from Union Carbide Corp.),bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate (e.g., ERL-4289™ fromUnion Carbide Corp.), bis(2,3-epoxycyclopentyl) ether (e.g., ERL-0400™from Union Carbide Corp.), aliphatic epoxy modified from polypropyleneglycol (e.g., ERL-4050™ and ERL-4052™ from Union Carbide Corp.),dipentene dioxide (e.g., ERL-4269™ from Union Carbide Corp.), epoxidizedpolybutadiene (e.g., Oxiron 2001™ from FMC Corp.), silicone resincontaining epoxy functionality, flame retardant epoxy resins (e.g.,DER-580™, a brominated bisphenol type epoxy resin available from DowChemical Co.), 1,4-butanediol diglycidyl ether of phenolformaldehydenovolak (e.g., DEN-431™ and DEN-438™ from Dow Chemical Co.), andresorcinol diglycidyl ether (e.g., Kopoxite™ from Koppers Company,Inc.), bis(3,4-epoxycyclohexyl)adipate (e.g., ERL-4299™ or UVR-6128™,from Union Carbide Corp.), 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexane-meta-dioxane (e.g., ERL-4234™ from Union Carbide Corp.),vinylcyclohexene monoxide 1,2-epoxyhexadecane (e.g., UVR-6216™ fromUnion Carbide Corp.), alkyl glycidyl ethers such as alkyl C₈ -C₁₀glycidyl ether (e.g., HELOXY Modifier 7™ from Shell Chemical Co.), alkylC₁₂ -C₁₄ glycidyl ether (e.g., HELOXY Modifier 8™ from Shell ChemicalCo.), butyl glycidyl ether (e.g., HELOXY Modifier 61™ from ShellChemical Co.), cresyl glycidyl ether (e.g., HELOXY Modifier 62™ fromShell Chemical Co.), p-ter butylphenyl glycidyl ether (e.g., HELOXYModifier 65™ from Shell Chemical Co.), polyfunctional glycidyl etherssuch as diglycidyl ether of 1,4-butanediol (e.g., HELOXY Modifier 67™from Shell Chemical Co.), diglycidyl ether of neopentyl glycol (e.g.,HELOXY Modifier 68™ from Shell Chemical Co.), diglycidyl ether ofcyclohexanedimethanol (e.g., HELOXY Modifier 107™ from Shell ChemicalCo.), trimethylol ethane triglycidyl ether (e.g., HELOXY Modifier 44™from Shell Chemical Co.), trimethylol propane triglycidyl ether (e.g.,HELOXY Modifier 48™ from Shell Chemical Co.), polyglycidyl ether of analiphatic polyol (e.g., HELOXY Modifier 84™ from Shell Chemical Co.),polyglycol diepoxide (e.g., HELOXY Modifier 32™ from Shell ChemicalCo.), bisphenol F epoxides (e.g., EPN-1138™ or GY-281™ from Ciba-GeigyCorp.), 9,9-bis[4-(2,3-epoxypropoxy)phenyl]fluorenone (e.g., Epon 1079™from Shell Chemical Co.).

Still other epoxy resins contain copolymers of acrylic acid esters orglycidol such as glycidylacrylate and glycidylmethacrylate with one ormore copolymerizable vinyl compounds. Examples of such copolymers are1:1 styrene-glycidylmethacrylate, 1:1methylmethacrylate-glycidylacrylate and a 62.5:24:13.5methylmethacrylate-ethyl acrylate-glycidylmethacrylate.

Other useful epoxy resins are well known and contain such epoxides asepichlorohydrins, alkylene oxides, e.g., propylene oxide, styrene oxide;alkenyl oxides, e.g., butadiene oxide; glycidyl esters, e.g., ethylglycidate.

The polymers of the epoxy resin can optionally contain otherfunctionalities that do not substantially interfere with cationicpolymerization at room temperature.

Blends of various epoxy-containing materials are also contemplated.Examples of such blends include two or more weight average molecularweight distributions of epoxy-containing compounds, such as lowmolecular weight (below 200), intermediate molecular weight (about 200to 10,000) and higher molecular weight (above about 10,000).Alternatively or additionally, the epoxy resin may contain a blend ofepoxy-containing materials having different chemical natures, such asaliphatic and aromatic, or functionalities, such as polar and non-polar.

Other types of useful materials having cationically active functionalgroups include vinyl ethers, oxetanes, spiro-orthocarbonates,spiro-orthoesters, and the like.

If desired, both cationically active and free radically activefunctional groups may be contained in a single molecule. Such moleculesmay be obtained, for example, by reacting a di- or poly-epoxide with oneor more equivalents of an ethylenically unsaturated carboxylic acid. Anexample of such a material is the reaction product of UVR-6105(available from Union Carbide) with one equivalent of methacrylic acid.Commercially available materials having epoxy and free-radically activefunctionalities include the Cyclomer™ series, such as Cyclomer M-100,M-101, or A-200 available from Daicel Chemical, Japan, and Ebecryl™-3605available from Radcure Specialties.

Suitable hydroxyl-containing materials can be any organic materialhaving hydroxyl functionality of at least 1, and preferably at least 2.Preferably, the hydroxyl-containing material contains two or moreprimary or secondary aliphatic hydroxyl groups (i.e., the hydroxyl groupis bonded directly to a non-aromatic carbon atom). The hydroxyl groupscan be terminally situated, or they can be pendent from a polymer orcopolymer. The molecular weight of the hydroxyl-containing organicmaterial can vary from very low (e.g., 32) to very high (e.g., onemillion or more). Suitable hydroxyl-containing materials can have lowmolecular weights, i.e. from about 32 to 200, intermediate molecularweight, i.e. from about 200 to 10,000, or high molecular weight, i.e.above about 10,000. As used herein, all molecular weights are weightaverage molecular weights. The hydroxyl-containing material canoptionally contain other functionalities that do not substantiallyinterfere with cationic polymerization at room temperature. Thus, thehydroxyl-containing materials can be non-aromatic in nature or cancontain aromatic functionality. The hydroxyl-containing material canoptionally contain heteroatoms in the backbone of the molecule, such asnitrogen, oxygen, sulfur, and the like, provided that the ultimatehydroxyl-containing material does not substantially interfere withcationic polymerization at room temperature. The hydroxyl-containingmaterial can, for example, be selected from naturally occurring orsynthetically prepared cellulosic materials. Of course, thehydroxyl-containing material is also substantially free of groups whichmay be thermally or photolytically unstable; that is, the material willnot decompose or liberate volatile components at temperatures belowabout 100° C. or in the presence of actinic light which may beencountered during the desired polymerization conditions for the freeradically active components of the pre-adhesive composition.

Representative examples of suitable hydroxyl-containing materials havinga hydroxyl functionality of 1 include alkanols, monoalkyl ethers ofpolyoxyalkyleneglycols, monoalkyl ethers of alkylene-glycols, and othersknown in the art.

Representative examples of useful monomeric polyhydroxy organicmaterials include alkylene glycols (e.g., 1,2-ethanediol;1,3-propanediol; 1,4-butanediol; 1,6-hexanediol; 1,8-octanediol;2-ethyl-1,6-hexanediol; bis(hydroxymethyl)cyclohexane;1,18-dihydroxyoctadecane; 3-chloro-1,2-propanediol); polyhydroxyalkanes(e.g., glycerine, tri-methylolethane, pentaerythritol, sorbitol) andother polyhydroxy compounds; 2-butyne-1,4-diol;4,4-bis(hydroxymethyl)diphenylsulfone; castor oil; and the like.

Representative examples of useful polymeric hydroxyl-containingmaterials include polyoxyethylene and polyoxypropylene glycols, andparticularly the polyoxyethylene and polyoxypropylene glycol diols andtriols having molecular weights from about 200 to about 10,000corresponding to a hydroxy equivalent weight of 100 to 5000 for thediols or 70 to 3300 for triols; polytetramethylene ether glycols such aspolytetrahydrofuran or "poly THF" of varying molecular weight;copolymers of hydroxypropyl and hydroxyethyl acrylates and methacrylateswith other free radical-polymerizable monomers such as acrylate esters,vinyl halides, or styrene; copolymers containing pendent hydroxy groupsformed by hydrolysis or partial hydrolysis of vinyl acetate copolymers,polyvinylacetal resins containing pendent hydroxyl groups; modifiedcellulose polymers such as hydroxyethylated and hydroxypropylatedcellulose; hydroxy-terminated polyesters; hydroxy-terminatedpolylactones, and particularly the polycaprolactones; fluorinatedpolyoxyethylene or polyoxypropylene glycols; and hydroxy-terminatedpolyalkadienes.

Useful commercially available hydroxyl-containing materials include the"TERATHANE" series of polytetramethylene ether glycols such as"TERATHANE" 650, 1000, 2000 and 2900 (available from du Pont de Nemours,Wilmington, Del.) the "PEP" series of polyoxyalkylene tetrols havingsecondary hydroxyl groups such as "PEP" 450, 550 and 650; "BUTVAR"series of polyvinylacetal resins such as "BUTVAR" B-72A, B-73, B-76,B-90 and B-98 (available from Monsanto Chemical Company, St. Louis,Mo.); and the "FORMVAR" series of resins such as 7/70, 12/85, 7/95S,7/95E, 15/95S and 15/95E (available from Monsanto Chemical Company); the"TONE" series of polycaprolactone polyols such as "TONE" 0200, 0210,0230,0240, 0300 and 0301 (available from Union Carbide); "PARAPLEXU-148" aliphatic polyester diol (available from Rohm and Haas,Philadelphia, Pa.), the "MULTRON" R series of saturated polyesterpolyols such as "MULTRON" R-2, R-12A, R-16, R-18, R-38, R-68 and R-74(available from Mobay Chemical Co.); "KLUCEL E" hydroxypropylatedcellulose having an equivalent weight of approximately 100 (availablefrom Hercules Inc.); "Alcohol Soluble Butyrate" cellulose acetatebutyrate ester having a hydroxyl equivalent weight of approximately 400(available from Eastman Kodak Co., Rochester, N.Y.); polyether polyolssuch as polypropylene glycol diol (e.g., "ARCOL PPG-425", "ArcolPPG-725", "ARCOL PPG-1025", "ARCOL PPG-2025", "ARCOL PPG-3025", "ARCOLPPG-4025" from ARCO Chemical Co.); polypropylene glycol triol (e.g.,"ARCOL LT-28", "ARCOL LHT-42", "ARCOL LHT 112", "ARCOL LHT 240", "ARCOLLG-56", "ARCOL LG-168", "ARCOL LG-650" from ARCO Chemical Co.); ethyleneoxide capped polyoxypropylene triol or diol (e.g., "ARCOL 11-27", "ARCOL11-34", "ARCOL E-351", "ARCOL E-452", "ARCOL E-785", "ARCOL E-786" fromARCO Chemical Co.); ethoxylated bis-phenol A; propylene oxide orethylene oxide--based polyols (e.g., "VORANOL" polyether polyols fromthe Dow Chemical Co.).

The amount of hydroxyl-containing organic material used in thecompositions of the invention may vary over broad ranges, depending uponfactors such as the compatibility of the hydroxyl-containing materialwith the epoxide and/or free radically polymerizable component, theequivalent weight and functionality of the hydroxyl-containing material,the physical properties desired in the final adhesive composition, thedesired speed of photopolymerization, and the like.

Blends of various hydroxyl-containing materials are particularlycontemplated in this invention. Examples of such blends include two ormore molecular weight distributions of hydroxyl-containing compounds,such as low molecular weight (below 200), intermediate molecular weight(about 200 to 10,000) and higher molecular weight (above about 10,000).Alternatively, or additionally, the hydroxyl-containing material cancontain a blend of hydroxyl-containing materials having differentchemical natures, such as aliphatic and aromatic, or functionalities,such as polar and non-polar. As an additional example, one may usemixtures of two or more poly-functional hydroxy materials or one or moremono-functional hydroxy materials with poly-functional hydroxymaterials.

The polymerizable material(s) can also contain hydroxyl groups and freeradically active functional groups in a single molecule. Examples ofsuch materials include hydroxyalkylacrylates andhydroxyalkylmethacrylates such as hydroxyethylacrylate,hydroxyethylmethacrylate; glycerol mono- or di-(meth)acrylate;trimethylolpropane mono- or di-(meth)acrylate, pentaerythritol mono-,di-, and tri-(meth)acrylate, sorbitol mono-, di-, tri-, tetra-, orpenta-(meth)acrylate; and2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane.

The polymerizable material(s) can also contain hydroxyl groups andcationically active functional groups in a single molecule. An exampleis a single molecule that includes both hydroxyl groups and epoxygroups.

The pre-adhesive composition further includes one or more polymerizationinitiators. The initiator may initiate only free radical polymerization,or it may be capable of initiating both free radical and cationicpolymerization. In the case of pre-adhesive compositions having bothfree radically active functional groups and cationically activefunctional groups, and designed for bonding cationically polymerizablecompositions such as epoxy-containing dental composites, it is possibleto include only a polymerization initiator capable of initiating freeradical polymerization in the pre-adhesive composition. The cationicallyactive groups of the pre-adhesive composition can then be polymerizedsimultaneously with the subsequently applied cationically polymerizablecomposition using the initiator capable of initiating cationicpolymerization that is included in the latter composition.

One class of initiators capable of initiating polymerization of freeradically active functional groups includes conventional chemicalinitiator systems such as a combination of a peroxide and an amine.These initiators, which rely upon a thermal redox reaction, are oftenreferred to as "auto-cure catalysts."

A second class of initiators capable of initiating polymerization offree radically active functional groups includes photoinitiators,optionally combined with a photosensitizer or accelerator. Suchinitiators typically are capable of generating free radicals foraddition polymerization at some wavelength between 200 and 800 nm.Examples include alpha-diketones, monoketals of alpha-diketones orketoaldehydes, acyloins and their corresponding ethers,chromophore-substituted halomethyl-s-triazines, chromophore-substitutedhalomethyl-oxadiazoles, and aryliodonium salts.

Palazzotto et al., U.S. Pat. No. 5,545,676, which is incorporated hereinby reference, describes ternary photoinitiation systems suitable forfree radical polymerization. These systems include an iodonium salt,e.g., a diaryliodonium salt; a sensitizer capable of light absorptionwithin the range of wavelengths between about 300 an about 1000nanometers (with visible light sensitizers such as camphorquinone beingpreferred); and an electron donor having an oxidation potential that isgreater than zero and less than or equal to that of p-dimethyoxybenzene(1.32 volts vs. S.C.E.).

Photoinitiator systems capable of initiating both free radical andcationic polymerization are described in Oxman et al., U.S. Ser. No.08/838,835 filed Apr. 11, 1997 entitled "Ternary Photoinitiator Systemfor Curing of Epoxy/Polyol Resin Compositions" and Oxman et al., U.S.Ser. No. 08/840,093 filed Apr. 11, 1997 entitled "Ternary PhotoinitiatorSystem for Curing of Epoxy Resins", both of which are assigned to thesame assignee as the present application and incorporated herein byreference. These photoinitiator systems include an iodonium salt (e.g.,an aryliodonium salt); a visible light sensitizer (e.g.,camphorquinone), and an electron donor. The systems have a photoinducedpotential greater than or equal to that of 3-dimethylaminobenzoic acidin a standard solution of 2.9×10⁻⁵ moles/g diphenyl iodoniumhexafluoroantimonate and 1.5×10⁻⁵ moles/g camphorquinone in 2-butanone.The photoinduced potential can be evaluated in the following manner. Astandard solution is prepared that contains 2.9×10⁻⁵ moles/g of diphenyliodonium hexafluoroantimonate and 1.5×10⁻⁵ moles/g of camphorquinone in2-butanone. A pH electrode is then immersed in the solution and a pHmeter is calibrated to zero mV. A test solution of the standard solutionand the compound is prepared next using the compound at a concentrationof 2.9×10⁻⁵ moles/g. This test solution is irradiated using blue lighthaving a wavelength of about 400 to 500 nm having an intensity of about200 to 400 mW/cm² for about 5 to 10 seconds at a distance of about 1 mm.Millivolts relative to the standard solution are then determined byimmersing the pH electrode in the test solution and obtaining a mVreading on the pH meter. Useful donors are those compounds that providea reading of at least 100 mV relative to the standard solution, andpreferably provide a gel time for the compositions that is at leastabout 30 to 40 percent shorter than for compositions that do not containthe donor. Higher mV readings are generally indicative of greateractivity.

In some instances there may be some uncertainty regarding the outcome ofthe above procedure. This may be due to questions or uncertainty arisingfrom the instrumentation employed, from the way the procedure wascarried out, or other factors, or one may wish to verify the suitabilityof a particular compound. A second test may be performed to verify theresult obtained by following the above procedure and resolve any suchuncertainty.

The second method involves the evaluation of the photoinduced potentialof an initiator system that includes the compound compared to a systemthat includes 3-dimethylamino benzoic acid. For this method, a standardsolution of 2.9×10⁻⁵ moles/g diphenyl iodonium hexafluoroantimonate,1.5×10⁻⁵ moles/g camphorquinone and 2.9×10⁻⁵ moles/g of3-dimethylaminobenzoic acid in 2-butanone is prepared. A pH electrode isthen immersed in the solution and a pH meter is calibrated to zero mV.The standard solution is irradiated with blue light having a wavelengthof between about 400-500 nm and an intensity of about 200 to 400 mW/cm²for about 5 to 10 seconds using a focused light source such as a dentalcuring light at a distance of about 1 mm. After light exposure, thepotential of the solution is measured by immersing a pH electrode in theirradiated standard solution and reading the potential in mV using a pHmeter. A test solution is then prepared using 2.9×10⁻⁵ moles/g ofdiphenyl iodonium hexafluoroantimonate, 1.5×10⁻⁵ moles/g ofcamphorquinone and 2.9×10⁻⁵ moles/g of the compound in 2-butanone. Thetest solution is irradiated and the photoinduced potential measuredusing the same technique as described for the standard solution. If thetest solution has a photoinduced potential that is the same as orgreater than that of the 3-dimethylaminobenzoic acid containing standardsolution, then the compound is a useful donor.

Also suitable are binary photoinitiation systems that include ansensitizer and an electron donor, or a sensitizer and an iodonium salt.The former initiate only free radical polymerization, while the latterinitiate both free radical and cationic polymerization.

The pre-adhesive compositions can also contain suitable adjuvants suchas fluoride sources, anti-microbial agents, accelerators, stabilizers,absorbers, pigments, dyes, viscosity modifiers, surface tensiondepressants and wetting aids, antioxidants, and other ingredients wellknown to those skilled in the art. The amounts and types of eachingredient should be adjusted to provide the desired physical andhandling properties before and after polymerization. In addition, theadjuvants should not be present in amounts that would detrimentallyaffect polymerization of any cationically active functional groups ofthe pre-adhesive composition, polymerization of a subsequently appliedcationically polymerizable composition, or both.

The pre-adhesive compositions are prepared by admixing, under "safelight" conditions, the various components of the compositions. Suitableinert solvents may be employed if desired when effecting the mixture.Examples of suitable solvents include acetone, dichloromethane, andacetonitrile.

Bonding Applications

The pre-adhesive composition is applied in the form of a relatively thinlayer to a hard tissue surface. Examples of hard tissue surfaces includeteeth (the component parts of which are enamel, dentin, and cementum),bone, fingernails, and hoofs. Preferred hard tissue surfaces includedentin and enamel. Prior to application of the pre-adhesive composition,the hard tissue surface may be pre-treated or primed to enhance adhesionto the hard tissue surface (e.g., using an acid etchant).

Following application to the hard tissue surface, the pre-adhesivecomposition is preferably polymerized to form an adhesive layer on thehard tissue surface. Preferably, polymerization is effected by exposingthe pre-adhesive composition to a radiation source, preferably a visiblelight source. Suitable visible light sources include a Visilux™ dentalcuring light commercially available from 3M Company of St. Paul, Minn.Such lights have an intensity of about 200 mW/cm² at a wavelength of400-500 nm. In the case of pre-adhesive compositions having both freeradically active functional groups and cationically polymerizable activegroups, exposure to the radiation source may effect polymerization ofthe free radically active groups alone, or both the free radically andcationically active groups, depending upon the choice of initiator.

In the case of thermal redox initiation systems (i.e., auto-curecatalysts), the components of the initiation system (e.g., peroxide andamine) are combined with each other, and then added to the remainder ofthe pre-adhesive composition. The resulting composition is then appliedto hard tissue and allowed to polymerize. Light activation is notnecessary.

Following polymerization to form the adhesive, a second composition isapplied to the adhesive. The adhesives are particularly useful forbonding dental compositions, especially where the dental compositioncontains cationically active functional groups such as epoxy groups orvinyl ether groups. The dental compositions may be filled or unfilled,and include dental materials such as direct esthetic restorativematerials (e.g., anterior and posterior restoratives), prostheses,sealants, veneers, cavity liners, crown and bridge cements, artificialcrowns, artificial teeth, dentures, and the like.

The term "composite" as used herein refers to a filled dental material.The term "restorative" as used herein refers to a composite which ispolymerized after it is disposed adjacent to a tooth. The term"prosthesis" as used herein refers to a composite which is shaped andpolymerized for its final use (e.g., as crown, bridge, veneer, inlay,onlay or the like) before it is disposed adjacent to a tooth. The term"sealant" as used herein refers to a lightly filled composite or to anunfilled dental material which is polymerized after it is disposedadjacent to a tooth. "Polymerizable" refers to curing or hardening thedental material, e.g., by free-radical, cationic, or mixed reactionmechanisms.

In the case of dental compositions containing cationically activefunctional groups, the dental composition is polymerized via a cationicmechanism following application to the bonding adhesive. Suitablepolymerization initiators incorporated into the polymerizable dentalcompositions include the initiators described above in the case of theadhesive composition that are capable of initiating both free radicaland cationic polymerization. Also suitable are cationic-only initiators.Examples include onium salts with complex metal halide anions (e.g.,diaryliodonium salts) and mixed ligand arene cyclopentadienyl metalsalts of complex metal halide anions. A commercially available exampleof the latter is Irgacure 261 which is available from Ciba Geigy.

The invention will now be described further by way of the followingexamples. Unless otherwise indicated, all parts and percentages are byweight.

EXAMPLES

Sample Preparation and Testing

Adhesives and composites were prepared by mixing individual ingredientstogether. Various combinations of adhesives and composites were thentested for adhesion to bovine teeth according to the following protocol.

Five bovine teeth of similar age and appearance were partially embeddedin circular acrylic discs. The exposed portion of each tooth was groundflat and parallel to the acrylic disc using Grade 120 silicon carbidepaper-backed abrasive mounted on a lapidary wheel in order to expose theenamel. Further grinding and polishing of the teeth was carried out bymounting Grade 320 silicon carbide paper-backed abrasive and then grade600 silicon carbide paper-backed abrasive on the lapidary wheel. Duringthe grinding and polishing steps, the teeth were continuously rinsedwith water.

The polished teeth were stored in distilled water, and used for testingwithin 2 hours after polishing. The polished teeth were removed from thewater and dried using a stream of compressed air. Next, SCOTCH BOND™MULTIPURPOSE ETCHANT (3M Co., St. Paul, Minn.) was applied to the enamelsurface for 15 seconds, rinsed with water, and then air-dried. A layerof pre-adhesive was then applied with a brush to the etched surface andexposed for 30 seconds to a "Visilux-2" dental curing light (3M Co., St.Paul, Minn.) to form a thin adhesive layer (approximately 50-150 micronsthick).

Previously prepared molds made from a 2 mm thick "Teflon" sheet with a 5mm diameter hole through the sheet were clamped to each polished toothso that the central axis of the hole in the mold was normal to thepolished tooth surface. The hole in each mold was filled with a visiblelight-polymerizable dental composite and exposed for 60 seconds toradiation from a "Visilux-2" dental curing light. The teeth and moldswere allowed to stand for about 5 minutes at room temperature, afterwhich they were stored in distilled water at 37° C. for 24 hours. Themolds were then carefully removed from the teeth, leaving a moldedbutton of dental composite attached to each tooth.

The adhesive strength between the composite and the tooth was evaluatedby mounting the acrylic disk in a holder clamped in the jaws of anInstron apparatus with the polished tooth surface oriented parallel tothe direction of pull. A loop of orthodontic wire (0.44 mm diameter) wasplaced around the button adjacent to the polished tooth surface. Theends of the orthodontic wire were clamped in the pulling jaw of theInstron, thereby placing the bond in shear stress (where "bond" refersto both the bond between the adhesive and the composite, and the bondbetween the adhesive and the tooth). Stress was applied using acrosshead speed of 2 mm/min. until the bond failed.

Five samples of each adhesive/composite combination were tested. Thereported adhesion value represents the average of five samples andreflects the point at which failure occurred at either theadhesive/tooth interface or the adhesive/composite interface, whicheveroccurred first.

Examples 1-8

Eight pre-adhesive compositions were prepared and subsequentlypolymerized to form adhesive compositions, as described above. Thecompositions contained the following ingredients:

Example 1

Resin: 50.0 parts of 6 moles ethoxylated Bisphenol A-dimethacrylate("BisEMA6"),

50.0 parts triethyleneglycol dimethacrylate ("TEGDMA").

Initiator: 0.25 parts camphorquinone ("CPQ"),

0.25 parts ethyl-p-dimethylaminobenzoate ("EDMAB"),

0.50 parts diaryliodonium hexafluoroantimonate (Sarcat™ CDI 012,Sartomer, Inc.).

Example 2

Resin: 50.0 parts Bisphenol A diglycidyl ether dimethacrylate("BisGMA"),

50.0 parts TEGDMA.

Initiator: 0.25 parts CPQ,

0.25 parts EDMAB,

0.50 parts CD1012.

Example 3

Resin: 61.9 parts BisGMA,

37.1 parts 2-hydroxyethyl methacrylate ("HEMA").

Initiator: 0.25 parts CPQ,

0.50 parts EDMAB,

0.40 parts diphenyl iodonium hexafluorophosphate.

Example 4

Single Bond™ Adhesive (3M Co., St. Paul, Minn.)

Example 5

Resin: 20.55 parts caprolactone modified cycloaliphatic monoepoxymono-methacrylate ("M-101" commercially available from Daicel Chemical,Japan),

57.53 parts BisGMA,

21.92 parts hexanedioldiacrylate ("HDDA").

Initiator: 0.25 parts CPQ,

0.25 parts EDMAB,

0.50 parts CD1012.

Example 6

Resin: 18.75 parts M-101,

52.5 parts BisGMA,

20.0 parts HDDA,

8.75 parts HEMA.

Initiator: 0.25 parts CPQ,

0.25 parts EDMAB,

0.50 parts CD1012.

Example 7

Resin: 72.0 parts 3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexanecarboxylate ("UVR6105"),

18.0 parts polytetrahydrofuran (MW=250) ("p(THF)"),

10.0 parts HEMA.

Initiator: 0.25 parts CPQ,

0.25 parts EDMAB,

0.50 parts CD1012.

Example 8

Resin: 80.0 parts UVR6105,

20.0 parts p(THF).

Initiator: 0.25 parts CPQ,

0.25 parts EDMAB,

0.50 parts CD1012.

Each adhesive composition was used to bond three different filled dentalcomposites to enamel, as described above. Each composite contained 21.5%by weight resin plus inititator and 78.5% by weight filler. Thecomposites contained the following ingredients (all amounts in weightpercent):

Methacrylate Composite

Resin: 50.0 parts BisGMA, 50.0 parts TEGDMA.

Initiator: 0.50 parts CPQ, 0.10 parts EDMAB, 1.25 parts CD1012.

Filler: Quartz filler as described above in the case of theEpoxy/Methacrylate composite.

Epoxy/Methacrylate Composite

Resin: 72.0 parts UVR6105, 18.0 parts p(THF), 10.0 parts M-101.

Initiator: 0.50 parts CPQ, 0.10 parts EDMAB, 1.25 parts CD1012.

Filler: Quartz filler prepared from a 90/10 blend of ball-milled groundquartz and Cab-O-Sil M-5 (Cabot Corp., Tuscola, Ill.). The averageparticle size of the filler was 2.25-3.15 microns.

Epoxy Composite

Resin: 42.0 parts UVR6105, 42.0 parts trimethylolpropane triglycidylether ("HELOXY-48"), 16.0% p(THF).

Initiator: 0.50 parts CPQ, 0.10 parts EDMAB, 1.25 parts CD1012.

Filler: Quartz filler as described above in the case of theEpoxy/Methacrylate composite.

A total of 24 adhesive/composite combinations were tested. The adhesionvalues, in MPa, are shown in Table I.

                  TABLE I                                                         ______________________________________                                                       Composite                                                      Exam-                          Epoxy/                                           ple Adhesive Functionality Methacrylate Methacrylate Epoxy                  ______________________________________                                        1     Methacrylate   12         6      3                                        2 Methacrylate/OH 11 14 14                                                    3 Methacrylate/OH 14 13 8                                                     4 Methacrylate/OH/ 15  2 0                                                     Urethane                                                                     5 Methacrylate/OH/Epoxy 11 14 14                                              6 Methacrylate/OH/Epoxy 11 15 14                                              7 Epoxy/OH/Methacrylate  0  0 0                                               8 Epoxy/OH  0  0 0                                                          ______________________________________                                    

These examples demonstrate the following:

(1) It is important to include free radically active functional groupsin the adhesives. Adhesives containing only cationically functionalepoxy groups failed to exhibit measurable adhesion regardless of thetype of composite. Similarly, regardless of the type of composite, it isdesirable to limit the amount of cationically active functional groupsin the adhesive, preferably such that the number of moles ofcationically active functional groups per gram of resin is no greaterthan about 0.002.

(2) When bonding composites having cationically active functionalgroups, it is desirable to avoid the presence of cationically inhibitinggroups such as urethane groups in quantities that can adversely affectcationic cure.

(3) Including functional groups such as hydroxyl groups in the adhesivecomposition that can covalently bond to components of the compositeimproves adhesion.

Examples 9-18 and Comparative Example 1

Eleven pre-adhesive compositions were prepared using M-101, BisGMA,HDDA, and UVR6105 as the basic ingredients, but varying the relativeamounts of each ingredient. In each case, the initiator contained 0.25parts CPQ, 0.25 parts EDMAB, and 0.50 parts CD1012. Each pre-adhesivecomposition was used to adhere a dental composite to a treated enamelsurface, as described above, after which the shear adhesion wasmeasured. The dental composite had the same composition as theEpoxy/Methacrylate Composite, described above. The results are shown inTable II.

                  TABLE II                                                        ______________________________________                                                                            moles                                       Exam-     epoxy/ Adhesion                                                     ple M-101 Bis-GMA HDDA UVR 6105 g resin (MPA)                               ______________________________________                                         9    0       50       50     0     0     14.3                                  10 20 50 30  0 0.0006 16.0                                                    11 40 50 10  0 0.0013 17.0                                                    12 50 50  0  0 0.0016 15.5                                                    13  0 50 30 20 0.0016 17.2                                                    14  0 50 10 40 0.0032 0.05                                                    15  0 50  0 50 0.0040 0.05                                                    16 60 40  0  0 0.0019 9.7                                                     17 10  0 90  0 0.0003 4.6                                                     18 60  0 40  0 0.0019 10.4                                                    Comp 1 100   0  0  0 0.0032 0.0                                             ______________________________________                                    

The results shown in Table II demonstrate the importance of includingfree radically active groups in the adhesive. For example, ComparativeExample 1, which did not contain any free radically active groups,failed to display measurable adhesion. The results further demonstratethe importance of minimizing the amount of cationically active groups inthe adhesive.

Other embodiments are within the following claims.

What is claimed is:
 1. A method for treating hard tissue comprising:(a)applying to hard tissue a composition comprising (i) a cationicallypolymerizable epoxy resin, (ii) a free radically polymerizable acrylicacid ester, methacrylic acid ester, or combination thereof, and (iii) aphotoinitiator capable of initiating free radical polymerization,wherein the number of moles of cationically polymerizable epoxy groupsper gram of said composition is no greater than about 0.0075; and (b)exposing said composition to polymerization conditions to form anadhesive bonded to said hard tissue.
 2. A method according to claim 1wherein said free radically polymerizable component (a)(ii) is selectedfrom the group consisting of methyl acrylate, methyl methacrylate, ethylacrylate, isopropyl methacrylate, n-hexyl acrylate, stearyl acrylate,allyl acrylate, glycerol diacrylate, glycerol triacrylate,ethyleneglycol diacrylate, diethyleneglycol diacrylate,triethyleneglycol dimethacrylate, 1,3-propanediol diacrylate,1,3-propanediol dimethyacrylate, trimethylolpropane triacrylate,1,2,4-butanetriol trimethacrylate, 1,4-cyclohexanediol diacrylate,pentaerythritol triacrylate, pentaerythritol tetraacrylate,pentaerythritol tetramethacrylate, sorbitol hexacrylate,bis[1-(2-acryloxy)]-p-ethoxyphenyldimethylmethane,bis[1-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylmethane,trishydroxyethyl-isocyanurate trimethacrylate, bis-acrylates andbis-methacrylates of polyethylene glycols of molecular weight 200-500,and mixtures thereof.
 3. A method according to claim 1 wherein saidcomposition comprises a hydroxy-functional acrylic acid ester, ahydroxy-functional methacrylic acid ester, or a combination thereof. 4.A method according to claim 1 wherein said composition comprises ahydroxy-functional component selected from the group consisting ofalkanols, monoalkyl ethers of polyoxyalkylene glycols, alkylene glycols,monoalkyl ethers of alkylene glycols, polyhydroxyalkanes,polyoxyethylene and polyoxypropylene glycols, polytetramethylene etherglycols, cellulosic materials, modified cellulose polymers,hydroxy-terminated polyesters, hydroxy-terminated polylactones,hydroxy-terminated polyalkadienes, and blends thereof.
 5. A methodaccording to claim 1 wherein said composition includes Bisphenol Adiglycidyl ether dimethacrylate.
 6. A method according to claim 5wherein said composition further includes triethyleneglycoldimethacrylate.
 7. A method according to claim 5 wherein saidcomposition further includes hydroxyethyl(meth)acrylate or glycerolmono- or di-(meth)acrylate.
 8. A method according to claim 5 whereinsaid composition further includes hexanedioldiacrylate.
 9. A methodaccording to claim 8 wherein said composition further includeshydroxyethyl(meth)acrylate or glycerol mono- or di-(meth)acrylate.
 10. Amethod according to claim 8 wherein said composition further includescaprolactone modified cycloaliphatic monoepoxy monomethacrylate.
 11. Amethod according to claim 8 wherein said composition further includes aniodonium salt, a visible light sensitizer, and an electron donor.
 12. Amethod for treating hard tissue comprising:(a) applying to hard tissue afirst polymerizable composition comprising (i) a free radicallypolymerizable acrylic acid ester, methacrylic acid ester, or combinationthereof, and (ii) a polymerization initiator capable of initiating freeradical polymerization, said first composition being essentially free ofpolymerizable components having cationically active functional groupsand being capable of forming an adhesive bonded to said hard tissue uponexposure to polymerization conditions; (b) applying a secondpolymerizable composition comprising (i) a cationically activefunctional group and (ii) a polymerization initiator capable ofinitiating cationic polymerization; and (c) exposing said secondcomposition to polymerization conditions to form a hardened compositionadhered to said hard tissue.
 13. A method according to claim 12 whereinsaid second composition comprises an epoxy resin.
 14. A method accordingto claim 13 wherein the polymerization initiator in each of the firstand second polymerizable compositions is a photoinitiator.
 15. A kitcomprising:(a) a composition comprising a cationically active functionalgroup, a free radically active functional group, and a photoinitiatorcapable of initiating free radical polymerization, wherein the number ofmoles of said cationically active functional groups per gram of saidcomposition is no greater than about 0.0075, wherein said compositionforms an adhesive capable of bonding to a tooth upon exposure topolymerization conditions; and (b) a dental material capable of bondingto said adhesive.
 16. A kit according to claim 15 wherein saidcomposition comprises an acrylic acid ester, a methacrylic acid ester,or a combination thereof.
 17. A kit according to claim 15 wherein saidcomposition comprises a hydroxy-functional acrylic acid ester, ahydroxy-functional methacrylic acid ester, or a combination thereof. 18.A kit to claim 15 wherein said composition comprises (a) an epoxy resinand (b) an acrylic acid ester, a methacrylic acid ester, or acombination thereof.
 19. A kit according to claim 15 wherein saidcomposition comprises an epoxy-functional acrylic acid ester,methacrylic acid ester, or a combination thereof.
 20. A kit according toclaim 15 further comprising one or more of the following: an etchant, aprimer, or an adhesion promoter.